Review: The Sixth Extinction

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From The Sixth Extinction, by Elizabeth Kolbert:


Very, very occasionally in the distant past, the planet has undergone change so wrenching that the diversity of life has plummeted. Five of these ancient events were catastrophic enough that they're put in their own category: the so-called Big Five. In what seems like a fantastic coincidence, but is probably no coincidence at all, the history of these events is recovered just as people come to realize that they are causing another one."

In a calm, reasoned, tone, Kolbert lays out the case that we are living through a mass extinction on Earth. We should be tearing out hair out, but we are not. Despite the intelligence of our species, humans are such obtuse creatures.

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Grade: B-

It's said that the way to boil a live frog is not to put it in a pot of hot water. "If a frog is put suddenly into boiling water, it will jump out, but if the frog is put in tepid water which is then brought to a boil slowly, it will not perceive the danger and will be cooked to death." (Wikipedia) That fable is relevant for two reasons. One, global warming is causing the Earth to be brought to a boil, metaphorically, but at a slow enough rate to keep people from taking action. What makes the fable not just a metaphor is that frogs, or amphibians in general, are already going extinct. As in past tense, not some future threat, but already dead and gone.

Frogs have been around longer than birds, longer than mammals, longer than dinosaurs. Kolbert tells the story of naturalists in Central America who were puzzled that amphibians had disappeared from habitats where they had been so abundant decades before that you couldn't walk through the rain forest without stepping on them. Study revealed that a deadly virus was the cause, a virus that probably was transported around the world by modern air travel or shipping. Globalization brings benefits in trade. It also bring threats to the natural habitat.

Most of us are familiar with the cause of the extinction of the dinosaurs — a meteor impact in Mexico's Yucatan Peninsula 66 million years ago. The exact timeline is still being researched, but that extinction event was sudden by almost any measure. Other extinctions were probably not quite so sudden. The extinction event of 450 million years ago is thought to have been brought about by glaciation. The extinction event of 250 million years ago is thought to have been caused by climate change in the opposite direction — a massive release of carbon into the air resulting in global warming.

You might think that the current mass extinction is somehow the result of climate change as well. You wouldn't be entirely wrong. A close cousin of climate change, ocean acidification, caused by carbon going not into the atmosphere, but into the ocean, is resulting in the deaths of coral reefs and the life that depends on them.

The current extinction event began tens of thousands of years ago, well before humans had begin altering the climate or ocean chemistry. There's a too strong correlation between humans settling the globe and extinction of the mega-fauna in locations as humans moved in. It begins about 40,000 years ago in Australia. It continues 10,000-15,000 years ago in the Americas. It happened more recently, in recorded history, with the moa in New Zealand, the auk on the coasts of the North Atlantic, and the dodo on the island of Mauritius, all hunted to extinction by early explorers and settlers.

As the case of amphibians shows, it's not just hunting that is causing extinctions. Besides the unwitting spread of viruses, there is also land clearing at fault. You might think that preserving more land in its natural state in parks and wilderness reserves is the solution to extinctions. Kolbert lays out a big problem with that solution. "A species that needs to migrate to keep up with rising temperatures, but is trapped in a forest fragment—even a very large fragment—is a species that isn't likely to make it. One of the defining features of the Anthropocene is that the world is changing in ways that compel species to move, and another is that it's changing in ways that create barriers—roads, clear-cuts, cities—that prevent them from doing so."

Scientists didn't even know about extinction until about 200 years ago, when the number of fossils being dug up and exhibited made it impossible to explain them away as just freak cases of existing species. Now, we are facing a world in which the extinction rate for some classes of life is a hundred thousand times higher than the natural extinction rate two hundred years ago. If that's not enough to lead you to tear your hair out, I don't know what will. There's no good reason to believe that somehow humans will be one of the few species to survive. Even if we do somehow get through a mass extinction, one of our own causing, we won't have many species with us on the other side.